The present invention relates to a shadow mask assembly manufacturing method and a cathode ray tube manufacturing method. In particular, the invention relates to a method of manufacturing a shadow mask which is a component of a cathode ray tube utilized for image display in a television receiver or the like. The shadow mask has minute holes through which an electron beam passes, and a support frame supports the shadow mask. The invention relates to a method of manufacturing the cathode ray tube with this shadow mask assembly incorporated therein.
As a television receiver, a flat type television receiver having a flat image display surface, or a flat television receiver is known. In contrast to the conventional television receiver, the image display surface of which has a gently curved convex surface, the flat type television receiver has an almost flat image display surface, which is regarded as being able to display an image with good visibility and little distortion.
The flat type television receiver employs a television tube having a flat image display surface for the purpose of image display. A shadow mask, which is arranged inside the fluorescent screen in the television tube and provided with minute holes through which an electron beam passes, has an almost flat plane.
In the shadow mask, the arrangement of the minute through holes exerts an influence on the positions and shape accuracy of individual bright spots of an image to be drawn by the electron beam. Therefore, the shadow mask must be accurately attached so as to be free from distortion and displacement.
In order to support the shadow mask in a flat plane state, the shadow mask is fixed in a tensioned state to a rectangular support frame by welding or similar means. There is a technique of fixing all four sides of the shadow mask to the support frame. However, it is regarded as more appropriate for supporting the shadow mask in a flat plane state to fix only the mutually opposite longer sides of the shadow mask to the support frame.
Specifically, for example, the unexamined Japanese Patent publication No. 08-167389 (Japanese Patent Application No. 06-309247) discloses that each side is pulled in a direction perpendicular to the side. The unexamined Japanese Patent publication No. 08-83563 (Japanese Patent Application No. 06-216314), the unexamined Japanese Patent publication No. 08-167376 (Japanese Patent Application No. 06-331451), and the unexamined Japanese Patent publication No. 09-92145 (Japanese Patent Application No. 07-271724) disclose that in order to remove wrinkles and slackness and reduce the clamping area, the shorter sides at four corners of a rectangular mask are pulled in four directions perpendicular to the shorter sides, or the mask is pulled in six directions. In other words, in addition to the four directions, center portions of two longer sides are pulled in two directions perpendicular to the longer sides, and then the mask is welded to a frame while the mask is tensioned. The unexamined Japanese Patent publication No. 10-188795 (Japanese Patent Application No. 08-343497), the unexamined Japanese Patent publication No. 10-188794 (Japanese Patent Application No. 08-343496), the unexamined Japanese Patent publication No. 11-185609 (Japanese Patent Application No. 09-358130), and the unexamined Japanese Patent publication No. 11-204026 (Japanese Patent Application No. 10-7850) disclose that in order to remove wrinkles and slackness, the shorter sides at four corners of a rectangular mask are pulled in four directions perpendicular to the shorter sides, and then the mask is welded to a frame while the mask is tensioned.
When fixing the mutually opposite longer sides of the shadow mask to the support frame, a tensioned state is provided by outwardly pulling the mutually opposite longer sides of the shadow mask.
However, there is an issue that the planarity of the shadow mask will be impaired when the shadow mask attached to the support frame is subjected to heat treatment through a baking process, even when the shadow mask is tensioned by sufficient tension forces. Specifically, it is often the case that a shadow mask that has undergone heat treatment comes to have a streak-shaped unevenness that extends in a direction perpendicular to the longer sides. In spite of the effort to increase the tension forces applied to the shadow mask, it has been difficult to completely suppress the occurrence of the aforementioned unevenness.
The object of the present invention is a shadow mask assembly manufacturing method and a cathode ray tube manufacturing method which enables a shadow mask to be attached to a support frame in an accurate planar state without unevenness.